Method for calibrating biomass sensors operating with impedance spectroscopy and use of a suspension for carrying out such a method

Abstract

A method is provided for calibrating impedance-spectroscopic biomass sensors that are embodied to detect information regarding the quantity and/or size of living cells in a biomass by means of an electric field having a periodically changing field directionA calibration suspension encompasses an electrically conductive viscously flowable or viscoelastic carrier substance and electrically conductive solid particles and/or solid semiconductor particles received therein.An electric field is generated having a periodically changing field direction, which acts on the calibration suspension.At least one permittivity value is detected, respectively representing a permittivity of the calibration suspension, in a context of at least two electric fields having different field direction change frequencies.A difference value is ascertained that represents a difference between the detected permittivity values.The difference value is compared with a reference value associated with the calibration suspension.

The invention claimed is: 
     
       1. A method for calibrating an impedance-spectroscopic biomass sensor that is embodied to detect information regarding the quantity and/or size of living cells in a biomass by means of an electric field having a periodically changing field direction, comprising the following steps:
 furnishing a calibration suspension, which is devoid of biological constituents in a form of living or dead cells and comprising an electrically conductive viscously flowable or viscoelastic carrier substance having an electrical conductivity in the range of 1 to 50 mS/cm, and electrically conductive solid particles and/or solid semiconductor particles received therein; 
 generating an electric field, having a periodically changing field direction at a frequency in the range of 50 kHz to 50 MHz, which acts on the calibration suspension; 
 detecting at least one permittivity value, respectively representing a permittivity of the calibration suspension, for each of at least two electric fields having different field direction change frequencies; 
 ascertaining a difference value representing a difference between the detected permittivity values; and 
 comparing the difference value with a reference value associated with the calibration suspension. 
 
     
     
       2. The calibration method according to  claim 1 , further comprising, before or during generation of the electric field, contact between the calibration suspension and at least a portion of the impedance-spectroscopic biomass sensor. 
     
     
       3. The calibration method according to  claim 2 , wherein contact between the calibration suspension and at least a portion of the impedance-spectroscopic biomass sensor includes wetting at least one sensor electrode of the impedance-spectroscopic biomass sensor with calibration suspension. 
     
     
       4. The calibration method according to  claim 2 , wherein contact between the calibration suspension and at least a portion of the biomass sensor encompasses wetting all sensor electrodes of the impedance-spectroscopic biomass sensor with calibration suspension. 
     
     
       5. The calibration method according to  claim 1 , further comprising a step of homogenizing the calibration suspension, by stirring and/or shaking the calibration suspension. 
     
     
       6. The calibration method according to  claim 5 , wherein the homogenizing step is performed before detection of the permittivity values. 
     
     
       7. The calibration method according to  claim 5 , wherein the homogenizing step is performed immediately before detection of the permittivity values. 
     
     
       8. The calibration method according to  claim 1 , further comprising adjusting the impedance-spectroscopic biomass sensor, or a data processing apparatus coupled to the impedance-spectroscopic biomass sensor in signal-transferring fashion, in accordance with a result of the comparison of the difference value with the reference value. 
     
     
       9. A method for impedance-spectroscopic detection of information regarding the quantity and/or size of living cells in a biomass, comprising the steps of:
 performing the calibration method according to  claim 1 ; 
 subsequently thereto: cleaning of the impedance-spectroscopic biomass sensor; 
 subsequently thereto: impedance-spectroscopic detection of information regarding the quantity and/or size of living cells in the biomass, by means of the impedance-spectroscopic biomass sensor and an electric field, generated thereby, having a periodically changing field direction. 
 
     
     
       10. The method for impedance-spectroscopic detection of information regarding the quantity and/or size of living cells in a biomass according to  claim 9 , further comprising subsequently thereto: performing the calibration method according to  claim 1 . 
     
     
       11. A calibration arrangement, comprising:
 an impedance-spectroscopic biomass sensor that is embodied to detect information regarding the quantity and/or size of living cells in a biomass by means of an electric field having a periodically changing field direction at a frequency in the range of 50 kHz to 50 MHz; 
 a calibration suspension being devoid of biological constituents in a form of living or dead cells and comprising an electrically conductive viscously flowable or viscoelastic carrier substance having an electrical conductivity in a range from 1 to 50 mS/cm and electrically conductive solid particles and/or solid semiconductor particles received therein, to calibrate the impedance-spectroscopic biomass sensor; and 
 a data processing device that is embodied to process sensor signals delivered operationally by the impedance-spectroscopic biomass sensor, and that is embodied in particular to carry out the method according to  claim 1 . 
 
     
     
       12. The calibration method according to  claim 1 , wherein the calibration suspension comprises an electrically conductive viscously flowable or viscoelastic carrier substance and electrically conductive solid particles and/or solid semiconductor particles received therein, to calibrate the impedance-spectroscopic biomass sensor that is embodied to detect information regarding the quantity and/or size of living cells in a biomass by means of an electric field having a periodically changing field direction.